Researchers from Long Island University, New York, studied carvacrol, a chemical in oregano, which when added to prostate cancer cells in the lab rapidly wiped them out.
Carvacrol could now be used itself as a treatment against cancer, or as the blueprint for an even more powerful drug.
Experts warned, though, that when oregano is eaten, it could be that carvacrol is digested before it can do any good, said media reports.
Oregano is commonly used as seasoning for pizzas
Supriya Bavadekar, researcher at Long Island, said: "Some researchers have previously shown that eating pizza may cut down cancer risk. This effect has been mostly attributed to lycopene, a substance found in tomato sauce, but we now feel that even the oregano seasoning may play role."
"If the study continues to yield positive results, this super-spice may present a very promising therapy for patients with prostate cancer. A significant advantage is that oregano is commonly used in food. We expect this to translate into a decreased risk of severe toxic effects," Bavadekar added.
Existing treatment for prostate cancer can lead to side-effects like incontinence and impotence.
These findings were presented at the Experimental Biology conference in San Diego, US.